1. Field of the invention
The present invention relates to a voltage/current converter circuit and a high-gain amplifying circuit, and particularly relates to a voltage/current converter circuit and a high-gain amplifying circuit wherein a high-gain amplifying circuit with improved linearity is realized by using MOS transistor differential pair circuits.
2. Description of the Related Art
Conventionally, in conjunction with increased speed of communication devices and data recording devices, high gain and improved linearity of amplifiers has been required.
FIG. 5 is a circuit diagram illustrating the circuit configuration of a conventional voltage/current converter circuit containing a MOS transistor differential pair circuit.
With the voltage/current converter circuit containing a conventional MOS transistor differential pair circuit shown in FIG. 5, the drain currents I.sub.1 and I.sub.2 are obtained by a later-described Expression (1).
Accordingly, with conventional voltage/current converter circuits, the action properties graph indicating the voltage/current conversion ratio thereof has exhibited a very narrow range where linearity is good.
Accordingly, a method for expanding the dynamic range by inserting a resistor between the sources of the MOS transistor differential pair has been conceived as means for securing the necessary linearity.
However, the above conventional method has adverse effects in that the conductance and gain of the amplifier are lowered. Accordingly, various methods for increasing linearity without inserting a resistor between the sources of the MOS transistor differential pair have been proposed.
FIG. 6 is a circuit diagram illustrating the circuit configuration of a conventional voltage/current converter circuit containing a MOS transistor differential pair circuit intending improved linearity.
The circuit shown in FIG. 6 realizes output current of i=I.sub.1 - I.sub.2 using a current mirror circuit, thus allowing the output current to be accurately proportionate to the input voltage.
However, with the conventional art, an N-MOS and P-MOS are used in junction as circuit components as can be understood from the voltage/current converter circuit shown in FIG. 6, so the power source voltage must be set high. Further, the output thereof is single output, which leads to the output current leaking to other circuits, consequently having markedly adverse effects on circuit operation.
As can be understood from the above examples, attempting to secure linearity with conventional voltage/current converter circuits using MOS transistor differential pair circuits results in high gain being unobtainable, and a differential output configuration cannot be used so the output current leaks to other circuits or circuit components. This has been a hindrance in advancement in application of high-frequency linear circuits with MOS transistors.